In WO01/46813 A1, there is described a communication system for downloading a structured document in which unit documents of the structured documents of related to one another hierarchically and are stored in a server device. A terminal device acquires and displays one of the structured documents. The server device and the terminal device are interconnected through a network to constitute a communication system. Further, the terminal device notifies the server device of the identifier of a document that the user gives an instruction to display. In view of this, the server device then sends the next document of the structured document for subsequent storage in the terminal device.
Further, in U.S. Pat. No. 5,895,476, there is described a design engine for automatic reformatting for design and media in support of automatic rendering multiple forms of media such as print.
In Girardot M. et al.: ‘Efficient representation and streaming of XML content over the Internet medium’, Multimedia And Expo, 2000, ICME 2000, 2000 IEEE International Conference On New York, N.Y., USA, 30 Jul.-2 Aug. 2000, Piscataway, N.J., USA, IEEE, U.S., 30 Jul. 2000, pages 67-70, XP010511404, ISBN: 0-7803-6536-4, there is described an efficient representation and streaming of XML content over the Internet medium.
Therefore, the further improvement of efficient web-enabled multimedia databases and middleware systems is a major topic in today's computer science research. The transmission and management of multimedia content differs essentially from handling numeric and character transmission data in communication systems and requires new strategies in handling multimedia data before transmission thereof.
This is particularly the case for so-called structured documents for which a transmission sequence is determined before transmission thereof. For structured documents it is assumed that related sub-documents have different hierarchy levels and that on each hierarchy level a partition and re-ordering of sub-documents may lead to severe fragmentations.
To explain this problem, further details of fragmentation will be explained in the following with respect to FIG. 1 to 4.
As shown in FIG. 1, a typical example of a structured document 10 comprises a plurality of sub-documents, e.g., a headline 12, a subtitle 14, an image 16 with a related caption 18, web-links 20 and different text sections 22, 24, 26, 28.
To improve transmission of such structured documents it has proven to be efficient to model the structure imposed on the structured document, e.g., using a tree-structure as shown in FIG. 2.
As shown in FIG. 2, the document as a whole is related to the root node. Further, the different sub-documents referred to above with FIG. 1 are modelled as nodes in the tree on lower levels of hierarchy. Here, one specific hierarchy level in the tree modelling a structured document will also be referred to as a level of detail node in the following.
A further concept applied to structured documents is relevance weighting. The main goal of relevance weighting is to provide an optimal transmission order for sub-documents during transmission, e.g., due to the possibly limited capacity in mobile communication environments like low band width.
Another example for the application of relevance weightings are end user interests where more relevant parts of structured documents should be delivered first. Therefore, relevance weightings are applied to identify content-bearing sub-documents, so that subsequently the document structure may be altered in a way that highly weighted sub-documents will be delivered first.
FIG. 3 shows the impact of relevance weightings on readability of documents after transmission thereof. The left figure of FIG. 3 is related to the natural reading sequence intended for natural reading of sub-documents, identified by the author of the structured document. Here, the abscissa identifies the number of sub-documents and the ordinate the related relevance weighting of each single sub-document. The right side of FIG. 3 shows the distribution of relevant weightings after reordering the sub-documents according to their relevance weighting.
As shown in FIG. 4 the simplistic application of relevance weightings to sub-documents before progressive transmission thereof may lead to a high grade of fragmentation of the structured documents as seen by the end user.
In particular, this is a problem for progressive transmission to a device having limited display capabilities, i.e., a mobile phone, a personal digital agent PDA, a portable computer, or a hybrid thereof. The display typically has a scroll bar 28 for triggering the display of the transmitted structured document. When scrolling the scroll bar from the upper side to the lower side, different parts of the transmitted structured document will be displayed to the user.
As shown in FIG. 4, relevance weightings may lead to a situation where, e.g., the image 18 shown in FIG. 1 is no longer displayed with the related head line. This fragmentation of the structured document leads to a significant decrease in perceivability after progressive transmission.